Optical recording medium

ABSTRACT

According to the present invention, there is provided an optical recording medium including at least an information recording layer and a reflective film in which the reflective film is comprised of an AgCu alloy thin film containing Cu the content of which is greater than or equal to 3.0 [atomic %] and less than or equal to 6.5 [atomic %]. Thus, the optical recording medium can be made inexpensive and weather resistance of the optical recording medium can be improved, thereby making it possible to avoid characteristics of the optical recording medium from being deteriorated even after it has been stored for a long time.

TECHNICAL FIELD

The present invention relates to an optical recording medium, such as aCD (Compact Disc) or a CD-ROM (CD-Read Only Memory), in which atranslucent reflective film and a reflective film can be improved inweather resistance more and which can be manufactured moreinexpensively.

BACKGROUND OF THE INVENTION

As optical recording medium for recording a variety of information suchas audio information and video information, various types of opticalrecording mediums are available in the form of a read-only opticalrecording medium such as a CD and a CD-ROM, a rewritable opticalrecording medium such as a magneto-optical disk and a phase-changeoptical disc and a write-once optical disc such as a CD-R made of anorganic material.

Information recording layers comprising these optical recording mediumsare indented to form thereon very small indentations such as phase pitsand pregrooves to record data information, a tracking servo signal andthe like.

Recently, there is an increasing demand for realizing optical recordingmedium capable of recording a larger amount of information, and a DVD(Digital Versatile Disc) of a two-layer structure having laminated firstand second information recording layers, for example, becomescommercially available.

FIG. 4 is a schematic cross-sectional view illustrating an opticalrecording medium 200 of a two-layer structure in which a firstinformation recording layer 231 and a second information recording layer232 are laminated to each other.

In the first information recording layer 231, a translucent reflectivefilm 223 made of a suitable material, such as Au, Si, AgPdCu and AgPdTi,is deposited on first very small indentations 211 which are formed atthe same time a first substrate 201 is molded by injection molding.

In the second information recording layer 232, a reflective film 224composed of a suitable thin film such as an Al thin film and an Al alloythin film, is deposited on second very small indentations 222 which areformed at the same time a second substrate 202 is molded by injectionmolding.

A transparent adhesive layer 203 laminates the first and secondsubstrates 201 and 202 with the first and second information recordinglayers 231 and 232 being facing to each other to form a two-layerinformation recording layer.

It is desirable that a set of optical heads should be used to reproduceor record or to reproduce and record (hereinafter simply referred to as“reproduce or record”) information from the first and second informationrecording layers 231 and 232 of the optical recording medium 200 withirradiation of laser beams from the same side of the optical recordingmedium, e.g., from the first substrate 201 side, for example, so that adrive apparatus therefor can be simplified, the optical heads can accessthese information recording layers 231 and 232 in a short time and cancontinuously record or reproduce these information recording layers.

When the optical head irradiates laser beams on the first and secondinformation recording layers 231 and 232 from the same side of theoptical recording medium to record or reproduce or record and reproducethe first and second information recording layers, the same optical headfocuses a laser beam L on the first information recording layer 231 torecord or reproduce or record and reproduce the first informationrecording layer 231 as shown by a solid line in FIG. 4 and the sameoptical head focuses a laser beam L on the second information recordinglayer 232 to record or reproduce or record and reproduce the secondinformation recording layer 232 as shown by a dotted line in FIG. 4.

In order that the same optical head may record or reproduce or recordand reproduce the first and second information recording layers 231 and232 with irradiation of laser beams, the first information recordinglayer 231 has the translucent reflective film 223 formed at its entranceside for inward laser beams to reflect part of irradiated laser beams sothat the first information recording layer 231 may be recorded orreproduced and to pass part of laser beams to allow part of laser beamsto travel to the second information recording layer 232 so that thesecond information recording layer 232 may be recorded or reproduced.

The transparent adhesive layer 203, made of an adhesive material havinga high transmittance with respect to laser beams, laminates the firstand second information recording layers 231 and 232 with a distance longenough to prevent their reproduced signal from interfering with eachother. Therefore, the optical heads can adjust objective lenses so as toproperly focus the laser beams on the positions corresponding to therespective information recording layers 231 and 232, thereby making itpossible to reproduce information from the respective informationrecording layers with high accuracy.

Design of films of the translucent reflective film 223 of the firstinformation recording layer becomes extremely important to realize theabove-mentioned signal reproducing method.

Au, Si, AgPdCu and AgPdTi are used as materials for forming thetranslucent reflective film 223 as described above.

So far these materials have been used as the materials of thetranslucent reflective film because they can satisfy opticalcharacteristics of the translucent reflective film 223 from a standpointof reflectance and transmittance relative to laser beams and they can beeasily deposited as thin films by sputtering.

However, Au encounters with a problem in which costs of materialsincrease. Although Si is relatively inexpensive, it is poor in adhesiveproperty with which it is bonded to the adhesive material comprising thetransparent adhesive agent layer 203 or it is bonded to the material ofthe substrate 201. Accordingly, silicon is not sufficiently reliable inmechanical deformation such as bending or warping or under severecircumstances with high humidity.

Further, when the Si film is compared with metal thin films, Si iseasily separated from the inside of a sputtering chamber where it isstuck in the sputtering process when the film is deposited, i.e.,so-called particles are easily produced so that an error rate is causedto be degraded.

The translucent reflective film needs a film thickness ranging from5[nm] to 25[nm] when it is made of metals or Si semiconductor materialsand so on that have been so far used to form ordinary translucentreflective films. This film thickness of the translucent reflective filmis thin as compared with a film thickness ranging from 35[mm] to 60[nm]of a reflective film of an ordinary compact disc, for example. Themetals or the Si semiconductor materials and the like for use in theordinary translucent reflective film are easily oxidized at theirsurface by influences exerted from the substrate 201 side after theyhave been stored for a long time and further after they have been storedunder circumstances with high temperature and high humidity.Accordingly, oxidation produced on the surface changes a reflectance ofthe translucent reflective film having such film thickness considerably,and this translucent reflective film is poor in weather resistance.

The translucent reflective film 223 is damaged not only by the influencefrom the substrate 201 side but also by oxidation from a contact portionwhere it is brought in contact with the transparent adhesive agent layer203. The oxidation from the contact portion changes the reflectance ofthe translucent reflective film and deteriorates the jitter of thereproduced signal unavoidably.

Apart from the problem of the above-mentioned oxidation, the translucentreflective film encounters with a phenomenon in which atoms are causedto move within the deposited film to increase thermal conductivity orreflectance of the translucent reflective film after the translucentreflective film has been left under circumstances with high temperaturewhere so-called annealed effect happens. This phenomenon becomes aserious problem depending upon compositions of the translucentreflective film.

The optical recording medium having the multilayer structure havevarious problems that should be solved when to make its translucentreflective film. To improve the weather resistance of the translucentreflective film and to reduce the cost thereof are important problemsthat should be solved when to make the optical recording medium havingthe multilayer structure commercially available on the market.

Weather resistance of the reflective film is important not only in thereflective film of the optical recording medium having the multilayerstructure but also in the reflective films for use in rewritable opticalrecording mediums such as a magneto-optical recording medium, aphase-change optical recording medium and a dye-system optical recordingmedium in which various material films are laminated as informationrecording layers. When the reflective film is degraded due to ageddeterioration such as oxidation, the deteriorated reflective filmchanges not only quality of the reproduced signal but also recordingconditions such as recording sensitivity.

The AgPdCu thin film or the AgPdTi thin film is inexpensive as comparedwith a simple substance of Au from a money standpoint and cannot beseparated from the adhesive material or the material of the substrateunlike the Si film.

Recently, a demand for higher recording density or larger recordingcapacity is increasing, and laser light with a short wavelength is usedas laser light for use in recording or reproducing information, wherebysurface recording density can be increased. In this case, recording pitsshould be formed with higher accuracy, and even though the amount inwhich the jitter in the reproduced signal is deteriorated is small tothe extent that it is allowable when the surface recording density islow, such very small amount of the deteriorated jitter raises a seriousproblem as the surface recording density increases.

Further, as the information recording layer is formed as the informationrecording layer having the two-layer structure as described above or theinformation recording layer is formed as an information recording layerhaving a multilayer structure of more than two layers, the translucentreflective film in each information recording layer at the entrance endside of inward light is progressively decreasing its film thickness morebecause reflectance and transmittance of each layer and the like shouldbe selected properly. Therefore, this translucent reflective film needshigher weather resistance.

Specifically, this translucent reflective film needs high weatherresistance to the extent that reflectance can be prevented from beingchanged and that the jitter in the reproduced signal can be preventedfrom being deteriorated under severe circumstances for a longer time.

Furthermore, a demand for manufacturing optical recording mediums moreinexpensively also is increasing more than before.

An object of the present invention is to provide an optical recordingmedium in which weather resistance of a translucent reflective film anda reflective film comprising information recording layers of an opticalrecording medium, in particular, weather resistance of the translucentreflective film with a special characteristic such as translucency canbe improved and in which a cost thereof can be reduced.

SUMMARY OF THE INVENTION

According to the present invention, there is provided an opticalrecording medium including at least an information recording layer and areflective film and in which the reflective film thereof is comprised ofan AgCu alloy thin film containing Cu the content of which is greaterthan 3.0 or equal to [atomic %] and less than or equal to 6.5[atomic %].

Moreover, according to the present invention, there is provided anoptical recording medium in which at least a first information recordinglayer and a second information recording layer are laminated to eachother and in which the first information recording layer has atranslucent reflective film formed thereon and the second informationrecording layer has a reflective film formed thereon and the translucentreflective film is comprised of an AgCu alloy thin film containing Cuthe content of which is greater than or equal to 3.0[atomic %] and lessthan 6.5 or equal to [atomic %].

In this arrangement, information is reproduced from the secondinformation recording layer with irradiation of light that has passedthrough the first information recording layer.

Moreover, according to the present invention, there is provided anoptical recording medium including at least an information recordinglayer and a reflective film and in which the reflective film thereof iscomprised of an AgCu containing alloy thin film containing Cu thecontent of which is greater than or equal to 2.0[atomic %] and less thanor equal to 9.0 [atomic %] and this AgCu containing alloy is made ofeither an AgCu containing ternary alloy or quaternary alloy containingone or two chemical elements of Al, Ti, Fe, Ni, Mo, W and whose totalcontent of the chemical elements is greater than or equal to 0.5[atomic%] and less than or equal to 8.1[atomic %].

Further, according to the present invention, there is provided anoptical recording medium in which at least a first information recordinglayer and a second information recording layer are laminated to eachother and in which the first information recording layer has atranslucent reflective film formed thereon, the second informationrecording layer has a reflective film formed thereon, the translucentreflective film thereof is composed of an AgCu containing alloy thinfilm containing Cu the content of which is greater than or equal to2.0[atomic %] and less than or equal to 9.0[atomic %] and this AgCucontaining alloy is made of an AgCu containing ternary alloy orquaternary alloy containing one or two chemical elements of Al, Ti, Fe,Ni, Mo, W and whose total content of the chemical elements is greaterthan or equal to 0.5[atomic %] and less than or equal to 8.1[atomic %].

In this arrangement, information is reproduced from the secondinformation recording layer with irradiation of light that has passedthrough the first information recording layer.

Moreover, according to the present invention, there is provided anoptical recording medium including at least an information recordinglayer and a reflective film and in which the reflective film thereof iscomprised of an AgCu containing alloy thin film containing Cu thecontent of which is greater than or equal to 1.5[atomic %] and less thanor equal to 9.0 [atomic %] and this AgCu containing alloy is made of anAgCuPd containing quaternary alloy or quinary alloy containing Pd thecontent of which is greater than or equal to 0.1[atomic %] and less thanor equal to 2.0[atomic %] and which contains one or two chemicalelements of Al, Ti, Fe, Ni, Mo, W and whose total content of thechemical elements is greater than or equal to 0.5[atomic %] and lessthan or equal to 8.1[atomic %].

Further, according to the present invention, there is provided anoptical recording medium in which at least a first information recordinglayer and a second information recording layer are laminated to eachother and in which the first information recording layer has atranslucent reflective film formed thereon, the second informationrecording layer has a reflective film formed thereon, the translucentreflective film is comprised of an AgCu containing alloy thin filmcontaining Cu the content of which is greater than 1.5 or equal to[atomic %] and less than 9.0 or equal to [atomic %] and this AgCu alloyis made of either an AgCuPd containing quaternary alloy or quinary alloycontaining Pd the content of which is greater than or equal to0.1[atomic %] and less than or equal to 2.0[atomic %] and which containsone or two chemical elements of Al, Ti, Fe, Ni, Mo, W and whose totalcontent of the chemical elements is greater than or equal to 0.5[atomic%] and less than or equal to 8.1 [atomic %].

In this arrangement, information is reproduced from the secondinformation recording layer with irradiation of light that has passedthrough the first information recording layer.

Then, in the above-mentioned optical recording medium including at leastthe first and second information recording layers, the first informationrecording layer is formed on a first substrate, the second informationrecording layer is formed on a second substrate, the first and secondsubstrates can be laminated to each other in such a manner thatinformation recording layers thereof may be facing to each other andinformation is reproduced from the first and second informationrecording layers with irradiation of light from the first substrateside.

As described above, according to the arrangement of the presentinvention, in the optical recording medium including the reflectivefilm, the reflective film thereof is composed of an AgCu alloy, an AgCucontaining alloy and further an AgCuPd containing alloy thin film and inthe optical recording medium including the reflective film and thetranslucent reflective film, at least the translucent reflective film iscomposed of an AgCu alloy, an AgCu containing alloy and further anAgCuPd containing alloy thin film. Therefore, it became possible toobtain an optical recording medium which can be made excellent inweather resistance and which can be made inexpensive.

Further, according to the present invention, in the AgCu containingalloy and AgCuPd containing alloy comprising the reflective film or thetranslucent reflective film or the reflective film and the translucentreflective film, since added chemical elements suitable for comprisingthese alloys are specified and their containing ratios are specified,the reflective film or the translucent reflective film or the reflectivefilm and the translucent reflective film can be improved in weatherresistance. Even after the optical recording medium has been stored fora long time under the conditions of high temperature and high humidity,for example, optical characteristics such as reflectance andtransmittance required by the information recording layer of the opticalrecording medium or recording density can be effectively avoided frombeing changed.

According to the arrangement of the present invention, as will becomeclear from descriptions which will be made later on, it is intended toobtain an optical recording medium which can exhibit higher weatherresistance and which can be made inexpensive, accordingly, which can bemanufactured inexpensively.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view showing an example of anoptical recording medium including two-layer information recordinglayers according to the present invention.

FIG. 2 is a schematic cross-sectional view showing another example of anoptical recording medium according to the present invention.

FIG. 3 is a schematic cross-sectional view showing a magneto-opticalrecording layer portion of a magneto-optical recording medium in anenlarged-scale.

FIG. 4 is a schematic cross-sectional view showing an example of anoptical recording medium according to the prior art.

FIG. 5 is a diagram showing a relationship between recording power and aCNR obtained before and after the storage tests.

FIG. 6 is a table (table 1-1) listing or enumerating arrangements ofsamples having various optical disc structures.

FIG. 7 is a table (table 1-2 enumerating characteristics of therespective samples shown in FIG. 6.

FIG. 8 is a table (table 2-1) enumerating arrangements of samples havingvarious optical disc structures.

FIG. 9 is a table (2-2) enumerating characteristics of the respectivesamples shown in FIG. 8.

FIG. 10 is a table (3-1) enumerating arrangements of samples havingvarious optical disc structures.

FIG. 11 is a table (table 3-2 enumerating characteristics of therespective samples shown in FIG. 10.

FIG. 12 is a table (table 4-1) enumerating arrangements of sampleshaving various optical disc structures.

FIG. 13 is a table (table 4-2) enumerating characteristics of therespective samples shown in FIG. 12.

FIG. 14 is a table (table 5-1) enumerating arrangements of sampleshaving various optical disc structures.

FIG. 15 is a table (table 5-2) enumerating characteristics of therespective samples shown in FIG. 14.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

An optical recording medium according to the embodiments of the presentinvention will be described below with reference to the drawings. It isneedless to say that the optical recording mediums according to thepresent invention are not limited to the following examples.

FIG. 1 is a schematic cross-sectional view showing an optical recordingmedium 10 according to the present invention.

In the optical recording medium 10, first and second substrates 1 and 2are laminated to each other through a transparent adhesive agent layer 3in such a manner that information recording layers 21 and 22 formed onthese substrates 1 and 2 maybe facing to each other. This opticalrecording medium is manufactured in accordance with a DVD (DigitalVersatile Disc) format having a two-layer structure in which the firstand second information recording layers 21 and 22 are laminated to eachother.

The first and second information recording layers 21 and 22 are indentedto have first and second very small indentations 11 and 12 correspondingto recording information. The first very small indentations 11 have atranslucent reflective film 13 deposited thereon to pass or reflect theirradiated light for recording and/or reproducing the optical recordingmedium. The second very small indentations 12 have a reflective film 14deposited thereon to reflect similar irradiated light.

The first substrate 1 can be molded by injection molding of a plasticmaterial such as polycarbonate that can pass the above-mentionedirradiated light. In this case, the first very small indentations 11also can be formed on the first information recording layer 21 on thefirst substrate 1 at the same time the first substrate 1 is molded byinjection molding.

The second substrate 2 can be similarly molded by injection molding of aplastic material such as polycarbonate regardless of the kind of plasticmaterials, such as a transparent plastic material or an opaque plasticmaterial. The second very small indentations 12 can be formed on thesecond information recording layer 22 at the same time the secondsubstrate 2 is molded.

A translucent reflective film 13 is deposited on the first very smallindentations 11 of the first information recording layer 21.

This translucent reflective film 13 is made of an AgCu alloy thin filmor an AgCu containing alloy thin film having a film thickness rangingfrom 10[nm] to 15[nm] such that it may reflect and pass part of theabove-mentioned irradiated light, e.g., laser beams.

AgCu alloy containing Cu the content of which is greater than or equalto 3.0[atomic %] and less than or equal to 6.5[atomic %] can be appliedas the AgCu alloy comprising the translucent reflective film 13.

The translucent reflective film 13 may be made of an AgCu containingternary alloy or quaternary alloy which is an AgCu alloy containing Cuthe content of which is greater than or equal to 2.0[atomic %] and lessthan or equal to 9.0[atomic %] and which contains one or two chemicalelements of Al, Ti, Fe, Ni, Mo, W and whose total content of thechemical elements is greater than or equal to 0.5[atomic %] and lessthan or equal to 8.1[atomic %].

Alternatively, the translucent reflective film 13 may be made of anAgCuPd containing quaternary alloy or quinary alloy which is an AgCucontaining alloy containing Cu the content of which is greater than orequal to 1.5[atomic %] and less than or equal to 9.0[atomic %] and whichcontains Pd the content of which is greater than or equal to 0.1[atomic%] and less than or equal to 2.0[atomic %] and which contains at leastone or more than two chemical elements of Al, Ti, Fe, Ni, Mo, W and inwhich the total content of these chemical elements is greater than orequal to 0.5[atomic %] and less than or equal to 8.1 [atomic %].

In the second information recording layer 22, a reflective film 14 isdeposited on the above-mentioned second very small indentations 12.

This reflective film 14 may be made of a metal material having a highreflectance, e.g., Au, an alloy whose principal component is Au, e.g.,Ag or an alloy whose principal component is Ag, or Pt or an alloy whoseprincipal component is Pt or Cu or an alloy whose principal component isCu and the like.

Moreover, in order to reduce the costs, the reflective film 14 may bemade of an Al alloy in which other metal material such as Si, Ti or Cris added to Al.

However, in order to improve weather resistance of the reflective filmand in order to reduce the cost of the reflective film, the reflectivefilm 14 may be made of the above-mentioned AgCu alloy, AgCu containingternary or quaternary alloy and AgCuPd containing quaternary or quinaryalloy having similar materials and compositions to those of theabove-mentioned translucent reflective film, and the film thickness ofthe reflective film can be selected in a range of from 35[nm] to 60[nm],for example.

The translucent reflective film 13 and the reflective film 14 can bothbe deposited by conventional sputtering, in general, magnetronsputtering.

A set of optical heads should be used to reproduce signals from thefirst and second information recording layers 21 and 22 or to recordsignals on the first and second information recording layers of theoptical recording medium 10 with irradiation of laser beams from thesame side of the optical recording medium 10, e.g., from the firstsubstrate 1 side in the arrangement shown in FIG. 1 so that a driveapparatus therefor can be simplified, the optical heads can access theseinformation recording layers 21 and 22 in a short time and cancontinuously record or reproduce these information recording layers.

When the optical head irradiates laser beams on the first and secondinformation recording layers from the same side of the optical recordingmedium 10 to reproduce or record the first and second informationrecording layers, the same optical head focuses a laser beam L on thefirst information recording layer 21 to reproduce or record the firstinformation recording layer as shown by a solid line in FIG. 1 and thesame optical head focuses a laser beam L on the second informationrecording layer 22 to reproduce or record the second informationrecording layer as shown by a dotted line in FIG. 1.

Next, a case in which the optical recording medium according to thepresent invention is applied to a magneto-optical recording medium willbe described.

FIG. 2 is a schematic cross-sectional view showing an example of amagneto-optical recording medium 100.

The magneto-optical recording medium 100 comprises a substrate 101 madeof a resin having transmittance such as polycarbonate, very smallindentations 102 such as pregrooves, formed on the substrate at the sametime the substrate is formed by injection molding, an information layer105 formed of a magneto-optical recording layer 104 on the very smallindentations 102 and a protective layer 106 formed on the informationlayer 105.

FIG. 3 is a schematic cross-sectional view showing a lamination layerstructure of the magneto-optical recording layer 104 of themagneto-optical recording medium 100 shown in FIG. 2.

The magneto-optical recording layer 104 may have a laminating layerarrangement shown in FIG. 3.

This magneto-optical recording layer 104 comprises the substrate 101,for example, on which a first dielectric layer 41 made of SiN_(x), forexample, and whose film thickness is approximately 40[nm], a recordinglayer 42 made of TbFeCo, for example, and whose film thickness isapproximately 15[nm], a translucent heat adjustment film 43 made of anAgCu containing alloy, which will be described later on, and whose filmthickness is approximately 10[nm], a second dielectric layer 44 made ofSiN_(x), for example, and whose film thickness is approximately 20[nm]and a reflective film 45 made of an AgCu containing alloy, which will bedescribed later on, and whose film thickness is approximately 40[nm] arelaminated, in that order.

The heat adjustment film 43 and the reflective film 45 shown in FIG. 3can be made of an AgCu alloy thin film or an AgCu containing alloy thinfilm similarly to the aforementioned translucent reflective film 13 andthe reflective film 14.

AgCu alloy containing Cu the content of which is greater than or equalto 3.0[atomic %] and less than or equal to 6.5[atomic %] can be appliedto the AgCu alloy.

Alternatively, the translucent reflective film and the reflective filmcan be made of an AgCu containing ternary alloy or quaternary alloywhich is an AgCu containing alloy containing Cu the content of which isgreater than or equal to 2.0[atomic %] and less than or equal to9.0[atomic %] and which contains one or two chemical elements of Al, Ti,Fe, Ni, Mo, W and in which the total content of the chemical elements isgreater than or equal to 0.5[atomic %] and less than or equal to8.1[atomic %].

Alternatively, the translucent reflective film and the reflective filmcan be made of an AgCuPd containing quaternary or quinary alloy which isan AgCu containing alloy containing Cu the content of which is greaterthan or equal to 1.5[atomic %] and less than or equal to 9.0[atomic %]and which contains Pd the content of which is greater than or equal to0.1[atomic %] and less than or equal to 2.0[atomic %] and which containsat least one or more than two chemical elements of Al, Ti, Fe, Ni, Mo, Wand in which the total contents of the chemical elements is greater thanor equal to 0.5[atomic %] and less than or equal to 8.1[atomic %].

The protective layer 106 may be made of a conventionalultraviolet-curing resin that can be cured by spin-coating.

Information is recorded on or reproduced from the magneto-opticalrecording medium 100 shown in FIG. 2 by laser beams irradiated on themagneto-optical recording medium from the side of the substrate 101.

Specifically, the optical head focuses a laser beam L on the informationlayer 105 as shown by a solid line in FIG. 2 to record information onthe magneto-optical recording medium or to reproduce information fromthe magneto-optical recording medium.

Next, in order to understand the characteristics of the opticalrecording medium according to the present invention, we had manufacturedsamples having respective disc structures including the embodiments ofthe optical recording medium according to the present invention,whereafter we had measured respective characteristics, i.e., weatherresistances.

In these samples, the reason that we had manufactured samples of discsof structures in which an information recording layer is formed on onlya one substrate (this sample of disc will hereinafter be referred to asa “single plate”) whereafter we have measured characteristics of thesesamples will be described below. That is, when the thickness of thesubstrate, for example, is selected to be 0.6[nm], since entire rigidityof such substrate is inferior to that of the structure in which firstand second information recording layers are sandwiched between twosubstrates, the substrate is warped considerably after it has beenstored by the storage test, and adhesion between the alloy thin filmcomprising the translucent reflective film, for example, and thesubstrate is lowered, thereby causing the alloy thin film and thesubstrate to be easily separated from each other. As a consequence, itbecomes able to estimate weather resistance very strictly.

Moreover, in the sample concerning the optical disc of the structure inwhich two substrates corresponding to the first and second substrates 1and 2 corresponding to the first and second information recording layers21 and 22 are laminated to each other, the alloy thin film correspondingto the reflective film 14 is made of an AlTi material of an ordinaryalloy thin film unlike the alloy thin film in the translucent reflectivefilm, because deterioration of such sample of the above optical disc inwhich alloy thin films of different nature are laminated to each otheris unavoidably accelerated under circumstances with high humidity andtherefore we can estimate weather resistance of such sample morestrictly. Specifically, in the samples of this structure in which twosubstrates are laminated to each other, when the translucent reflectivefilm and the reflective film are both made of an AgCu alloy, an AgCucontaining alloy or an AgCuPd containing alloy, these samples canexhibit more excellent weather resistance.

That is, we have studied characteristics of the materials of thetranslucent reflective films more strictly based upon the respectivesamples.

[Sample 1]:

First, a 0.6[nm]-thick substrate was molded by injection molding ofpolycarbonate.

At the same time the substrate was molded, very small indentations,i.e., pit data rows modulated by using an EFM code in which a trackpitch was 0.74[μm], a depth of pit was 110 [nm] and a shortest pitlength was 0.44[μm] were formed on one major surface of this substrate.

A translucent reflective film made of Ag_(100-x)Cu_(x) (x is atomic %)where x=3.0 and whose film thickness ranges from 10[nm] to 15[nm] wasdeposited on the substrate in which the pit data rows are formed bymagnetron sputtering, thereby resulting in the first informationrecording layer 21 being formed.

Next, a protective layer was formed over the whole surface of the AgCualloy translucent reflective film by spin-coating and curing aultraviolet-curing resin.

[Sample 2]:

In a similar arrangement to that of the sample 1, a translucentreflective film had a composition in which x=6.5.

[Sample 3] (Inventive Example 1):

This sample had a structure corresponding to that shown in FIG. 1 and inwhich the first and second substrates 1 and 2 including the first andsecond information recording layers 21 and 22 are laminated to eachother.

In this case, the first substrate 1 having the arrangement similar tothat of the substrate of the sample 1 was prepared. An AgCu alloy thinfilm having a composition of Ag_(100-x)Cu_(x) where x=3.0 was depositedon the first substrate by magnetron sputtering to deposit thetranslucent reflective film 13 having the film thickness ranging from 10to 15[nm], thereby resulting in the first information recording layer 21being formed.

On the other hand, there was manufactured the second substrate 2 havingthe arrangement similar to that of the first substrate 1. On the secondsubstrate 2, there was deposited the reflective film 14 made of an AlTialloy thin film having a film thickness 50[nm] by magnetron sputtering,thereby resulting in the second information recording layer 22 beingformed.

Then, the first and second substrates 1 and 2 were laminated to eachother by using a ultraviolet-curing resin as a transparent adhesiveagent in such a manner that their information recording layers 21 and 22may be facing to each other, thereby resulting in an optical disc havinga laminated structure being manufactured.

In this connection, the film thickness of the AgCu containing alloy filmdeposited on the first substrate 1 is selected in such a fashion that,when an Al alloy film having a film thickness ranging from 35 to 60[nm]or an Ag alloy film having a film thickness ranging from 30 to 60[nm] isformed as the reflective film 14 on the second substrate 2 by laserbeams having a wavelength of 660[nm], reflectance of the firstinformation recording layer 21 and that of the second informationrecording layer 22 may become nearly equal to each other.

[Sample 4]

COMPARATIVE EXAMPLE 1

Although this sample had an arrangement similar to that of the sample 1and was manufactured by a similar method, its alloy thin film has analloy atomic composition expressed as Ag_(100-x)Cu_(x) where x=2.0.

[Sample 5]

COMPARATIVE EXAMPLE 2

Although this sample had an arrangement similar to that of the sample 1and was manufactured by a similar method, its alloy thin film has analloy atomic composition expressed as Ag_(100-x)Cu_(x) where x=7.0.

[Sample 6]

COMPARATIVE EXAMPLE 3

Although this sample had an arrangement similar to that of the sample 1and was manufactured by a similar method, its alloy thin film has analloy atomic composition expressed as Ag_(100-x)Cu_(x) where x=9.0

[Sample 7]

COMPARATIVE EXAMPLE 4

Although this sample had an arrangement similar to that of the sample 1and was manufactured by a similar method, instead of itsAg_(100-x)Cu_(x) alloy thin film, an Si film having a film thicknessranging from 10 to 15[nm] was deposited on the first substrate 1 bymagnetron sputtering, thereby resulting in the first informationrecording layer 21 being formed.

Next, similarly to the first substrate 1, the reflective film 14 made ofan AlTi alloy thin film having a film thickness of 50[nm] was depositedon the second substrate 2 by magnetron sputtering, thereby resulting inthe second information recording layer 22 being formed.

Similarly to the sample 3, these first and second substrates 1 and 2were laminated to each other by using the ultraviolet-curing resin asthe transparent adhesive agent in such a manner that their informationrecording layers 21 and 22 may be facing to each other, whereby theoptical disc of the laminated structure was manufactured.

[Sample 8]

COMPARATIVE EXAMPLE 5

Although this sample had the arrangement similar to that of the sample 1and was manufactured by a similar method, an Ag film having a filmthickness ranging from 10 to 15[nm] was deposited as its translucentreflective film.

The storage test under circumstances with high temperature and highhumidity was effected on the above-mentioned respective samples 1 to 8and reflectances [%] and jitter [%] of the respective informationrecording layers 21, 22 were measured, whereby ratios [%] at whichreflectances of the information recording layers are changed before andafter the storage test were calculated.

In the storage test under circumstances with high temperature and highhumidity, the optical discs of the respective samples were left within astorage bath with RH circumstances having a temperature of 85° C. and ahumidity of 90% for 100 hours.

Jitter values were measured by an optical pickup having a semiconductorlaser having a wavelength of 660[nm] and an objective lens having anumerical aperture of 0.60.

Tables 1-1 and 1-2 of FIGS. 6 and 7 show compositions (atomic %) ofmaterials of deposited translucent reflecting films, optical discstructures, measured results of reflectances [%] and jitters [%] of therespective information recording layers 21, 22 obtained before and afterthe storage test and amounts with which reflectances of the informationrecording layers were changed before and after storage test with respectto the respective samples 1 to 8.

In the tables, R₁[%] shows reflectances of the first informationrecording layers 21 of the respective samples (optical discs) of thesingle plate structure and the laminating structures obtained at theinitial stage, i.e., reflectances obtained before the storage test, andR₃[%] shows reflectances obtained after the storage tests of thesesamples.

In the tables, R₂[%] shows reflectances of the second informationrecording layers 22 of the samples (optical discs) of the laminatingstructures obtained at the initial stage, and R₄[%] shows reflectancesof the second information recording layers of these samples obtainedafter the storage test.

Further, the amount with which the reflectance is changed before andafter the storage test is shown by |R₁-R₃| [%].

It is to be understood that, with respect to the samples 1 to 3 in whichAg_(100-x)Cu_(x) (3≦x≦6.5) thin films were deposited on the informationrecording layers of the optical discs of the single plate structures andthe first information recording layers 21 of the optical discs of thelaminating structures as shown on the tables 1 (FIGS. 6 and 7), thechanges of the reflectances obtained before and after the storage testcould be decreased to less than 1.0[%], the changes of the jittersobtained before and after the storage test could be suppressed to beless than 1[%] so that the optical characteristics with excellentweather resistance could be obtained.

In the samples 4 to 7 (comparative examples 1 to 4) the amounts in whichthe reflectances were changed before and after the storage test hadexceeded 1.0[%]. In the sample 8 (comparative example 5), there arose aproblem that the jitter value obtained after the storage test wereincreased so that a signal could not be reproduced with stability.

Next, there were manufactured samples 9 to 39 in which either an AgCu(Al, Ti, Fe, Ni, Mo, W) ternary alloy or quaternary alloy containing Cuthe content of which is greater than or equal to 2.0[atomic %] and lessthan or equal to 9.0[atomic %] and which contains one or two chemicalelements of Al, Ti, Fe, Ni, Mo, W and in which the total content of thechemical elements is greater than or equal to 0.5[atomic %] and lessthan or equal to 8.1[atomic %] was deposited on the informationrecording layers.

[Sample 9] to [Sample 31]:

These samples were optical discs of single plates having arrangementssimilar to that of the sample 1 and were manufactured by a similarmethod. In these samples, instead of the AgCu alloy film deposited onthe substrate 1, the translucent reflective film 13 was made of anAg_(100-x-y)Cu_(x)A_(y) (A is one or two chemical elements of Al, Ti,Fe, Ni, Mo, W and x, y represent atomic % respectively) thin film havinga film thickness ranging from 10 to 15[nm] where 2≦x≦9.0 and 0.5≦y≦8.1.

[Sample 32] (Inventive Example 2) to [Sample 38] (Inventive Example 8):

These samples of the laminating structures of the first and secondsubstrates 1 and 2 having the first and second information recordinglayers 21 and 22 shown in FIG. 1 had arrangements similar to that of thesample 3 and were manufactured by the similar method. In these samples32 to 38, the translucent reflective film 13 on the first substrate 1was made of an Ag_(100-x-y)Cu_(x)A_(y) (A is one or two chemicalelements of Al, Ti, Fe, Ni, Mo, W and x, y represent atomic %respectively) alloy thin film having a film thickness ranging from 10 to15[nm] where 2≦x≦9 and 0.5≦y≦8.1.

[Sample 39]

COMPARATIVE EXAMPLE 6

This sample had a similar arrangement to that of the sample 1 and wasmanufactured by a similar method. In this sample 39, the translucentreflective film 13 there of has an alloy atomic composition expressed asAg_(100-x-y)Cu_(x)A_(y) (A was Al and Ti) where x=5.4 and y=8.5.

Other conditions were similar to those of [sample 1] and the sample ofthe optical disc of the single plate structure was manufactured.

With respect to the above-mentioned samples 9 to 39, the compositions(atomic %) of the materials forming their translucent reflecting filmsand the optical disc structures are shown on tables 2-1 and 3-1 of FIGS.8 and 10. The similar storage test under circumstances with hightemperature and high humidity was effected on these samples and testresults are shown on tables 2-2 and 3-2 of FIGS. 9 and 11.

In the samples 9 to 38 having the information recording layers of theoptical disc of the single plate structures and the first informationrecording layers 21 of the optical disc of the laminating structures inwhich alloy atomic compositions were expressed asAg_(100-x-y)Cu_(x)A_(y) (A is at least one of Al, Ti, Fe, Ni, Mo, W) andin which 2≦x≦9 and 0.5≦y≦8.1, the amounts in which the reflectances werechanged before and after the storage test could be decreased to be lessthan 1.0[%] and the amounts in which the jitters were changed before andafter the storage test could be suppressed to be less than 1[%]. Inparticular, there could be obtained optical characteristics withexcellent weather resistance.

On the other hand, in the sample 39 (comparative example 6), the amountsin which the reflectances were changed before and after the storage testexceeded 1.0[%] and the weather resistance was deteriorated.

Next, there are shown samples (optical discs) in which translucentreflective films made of AgCuPd containing quaternary alloy or quinaryalloy containing Cu the content of which is greater than 1.5[atomic %]and less than 9.0[atomic %] and which contains one or two chemicalelements of Al, Ti, Fe, Ni, Mo, W and in which the total content of thechemical elements is greater than or equal to 0.5[atomic %] and lessthan or equal to 8.1[atomic %] and which contains Pd the content ofwhich is greater than or equal to 0.1[atomic %] and less than or equalto 2.0[atomic %] were deposited on the information recording layers.

[Sample 40] to [Sample 60]:

Although these samples had the single plate structures having similarstructures to that of the sample 1 and were manufactured by the similarmethod, their translucent reflective films 13 had alloy atomiccompositions expressed as Ag_(100-x-y-z)Pd_(z)Cu_(x)A_(y) (A is one ofAl, Ti, Fe, Ni, Mo and W and x, y, z represent atomic % respectively)where 1.5≦x≦9.0, 0.5≦y≦8.1 and 0.1≦z≦2.0.

[Sample 61] (Inventive Example 9) to [Sample 65] (Inventive Example 13):

Although these samples had similar structures to that of the sample 3(inventive example 1) and were manufactured by the similar method, theirtranslucent reflective films 13 had alloy atomic compositions expressedas Ag_(100-x-y-z)Pd_(x)Cu_(x)A_(y) (A is one of Al, Ti, Fe, Ni, Mo and Wand x, y, z represent atomic % respectively) where 1.5≦x≦9.0, 0.5≦y≦8.1and 0.1≦z≦2.0.

[Sample 66]

COMPARATIVE EXAMPLE 7

Although this sample had a similar structure to that of the sample 1 andwas manufactured by the similar method, its translucent reflective film13 had an alloy atomic composition expressed asAg_(100-x-y-z)Pd_(z)Cu_(x)A_(y) (A is Al) where x=4.0, y=9.0 and z=0.9.

[Sample 67]

COMPARATIVE EXAMPLE 8

Although this sample had a similar structure to that of the sample 1 andwas manufactured by the similar method, its translucent reflective film13 had an alloy atomic composition expressed asAg_(100-x-y-z)Pd_(z)Cu_(x)A_(y) where x=1.5, y=0.0 and z=0.9.

[Sample 68]

COMPARATIVE EXAMPLE 9

Although this sample had a similar structure to that of the sample 1 andwas manufactured by the similar method, its translucent reflective film13 had an alloy atomic composition expressed asAg_(100-x-y-z)Pd_(z)Cu_(x)A_(y) where x=1.5, y=0.0 and z=0.9.

[Sample 69]

COMPARATIVE EXAMPLE 10

Although this sample had a similar structure to that of the sample 3 andwas manufactured by the similar method, its translucent reflective film13 had an alloy atomic composition expressed asAg_(100-x-y-z)Pd_(z)Cu_(x)A_(y) where x=1.5, y=0.0 and z=0.9.

[Sample 70]

COMPARATIVE EXAMPLE 11

Although this sample had a similar structure to that of the sample 3 andwas manufactured by the similar method, its translucent reflective film13 had an alloy atomic composition expressed asAg_(100-x-y-z)Pd_(z)Cu_(x)A_(y) where x=4.0, y=0.0 and z=0.9.

With respect to the optical discs of the above-mentioned samples 57 to70, tables 5-1 and 5-2 of FIGS. 14 and 15 show compositions (atomic %)of materials forming their translucent reflective films, optical discstructures and test results obtained after the similar storage testseffected under circumstances with high temperature and high humidity.

As shown on the tables 5-1 and 5-2 of FIGS. 14 and 15, in the samples 40to 65 in which the first information recording layers 21 of the singleplate structures and the laminating structures have alloy atomiccompositions expressed as Ag_(100-x-y-z)Pd_(z)Cu_(x)A_(y) where A is oneor two kinds of chemical elements of Al, Ti, Fe, Ni, Mo, W and1.5≦x≦9.0, 0.5≦y≦8.1 and 0.1≦z≦2.0, the amount with which thereflectances were changed before and after the storage test could bedecreased to be less than 1.0[%], the amount in which the jitters werechanged before and after the storage test could be suppressed to be lessthan 1[%], and in particular, optical characteristics with excellentweather resistance could be obtained.

In the sample 66 (comparative example 7), the jitter value obtainedafter the storage test was increased so that a signal could not bereproduced with high stability.

In the optical discs shown in the sample 67 (comparative example 8) tothe sample 70 (comparative example 11), the amounts in whichreflectances are changed before and after the storage test exceeded1.0[%] and weather resistance was deteriorated.

As is clear from the above description, according to the presentinvention, the AgCu alloy thin film or the AgCu containing alloy thinfilm is applied to the information recording layer, the composition ofthe above alloy thin film is specified, the chemical element of theabove composition is selected and the content of such chemical elementis specified, whereby the weather resistance of the informationrecording layer can be improved, the amounts in which the opticalcharacteristics such as the reflectance or the transmittance required bythe information recording layer of the optical recording medium arechanged after the optical recording medium has been stored for a longtime under conditions with high temperature and high humidity can besuppressed to be low and the deterioration of the jitter can be avoidedeffectively. Moreover, the cost of the optical recording mediumaccording to the present invention can be reduced as compared with thatof the prior-art optical recording medium.

While the optical discs of ROM (Read Only Memory) type have beenillustrated so far in the above-mentioned respective samples, thepresent invention is not limited to those examples and can be alsoapplied to rewritable optical discs, such as a magneto-optical recordingdisc and a phase-change recording disc. When the AgCu alloy thin filmcomprising the information recording layer of the present invention isapplied to the reflective film or the heat structure film, the weatherresistance can be improved and the amount in which the recording densityis changed due to aged deterioration caused after the optical disc hadbeen stored for a long time can be decreased. As a result, stablerecording becomes possible, and the jitter can be effectively avoidedfrom being deteriorated.

For example, the present invention was applied to the magneto-opticalrecording medium 100 shown in FIG. 3 and change of recording sensitivitywas measured.

The magneto-optical recording medium 100 comprises the substrate 101 onwhich there are laminated the first dielectric layer 41 made of SiN_(x)having a film thickness of 40 [nm], the recording layer 42 made ofTbFeCo having a film thickness of 15[nm], the heat adjustment film 43formed of the translucent reflective film made of AgCu containing alloyhaving a film thickness of approximately 10[nm], the second dielectriclayer 44 made of SiN_(x) having a film thickness of approximately 20[nm]and the reflective film 45 made of AgCu containing alloy having a filmthickness of approximately 40[nm], in that order.

We had manufactured magneto-optical disk samples in which the heatadjustment film 43 and the reflective film 45 were formed ofAgPd_(0.9)Cu_(1.5) alloy thin films and magneto-optical disks formed ofAgCu_(0.9)Ti_(1.7) alloy thin films.

In this case, a mark length of 0.3 [μm] was recorded on themagneto-optical recording layer 104 deposited on the substrate 101 inwhich recording guide grooves, formed of so-called lands and grooves,having a track pitch of 0.80 [μm] and a groove depth of 30[nm] wereformed under respective conditions in which a wavelength of laser lightwas selected to be 405[nm], a numerical aperture of an objective lenswas selected to be 0.60 and a linear velocity was selected to be4.6[m/s] by a method called magnetic field modulation recording, and wehad measured relationships between recording power and CNRs ofreproduced signals obtained before and after the above-mentioned storagetest.

FIG. 5 shows measured results. In FIG. 5, solid squares and open squaresshow measured results obtained before and after the storage tests hadbeen effected on the magneto-optical disks in which AgPd_(0.9)Cu_(1.5)alloy thin films were deposited, and solid circles and open circles showmeasured results obtained before and after the storage tests had beeneffected on the magneto-optical disks in which AgCu_(0.9)Ti_(1.7) alloythin films were deposited.

As shown in FIG. 5, in the magneto-optical disks in which theAgPd_(0.9)Cu_(1.5) alloy thin films were deposited, recording powerobtained after the storage test under high temperature and high humidityconditions was shifted in the increasing direction of approximately 10%.That is, after the magneto-optical disks had been left under hightemperature and high humidity conditions, atoms in the deposited thinfilm are caused to move to increase density of the thin film with theresult that thermal conductivity increases and energy loss increases.

On the other hand, in the magneto-optical disk in which theAgCu_(0.9)Ti_(1.7) alloy thin film in the magneto-optical disk accordingto the example of the optical recording medium of the present inventionwas deposited, after the storage test under high temperature and highhumidity conditions, it is to be understood that recording power is notincreased, energy loss is small and that the film characteristic isextremely excellent in weather resistance.

In general, thermal conductivity of metal material may increase in themetal material having higher reflectance, and conversely, thermalconductivity of metal material may decrease as its reflectance maydecrease. Moreover, recording density may decrease as thermalconductivity of metal material may increase. Stated otherwise, recordingdensity may increase as thermal conductivity may decrease.

It is possible to estimate changes of recording sensitivity by measuringthe amounts in which reflectances of the reflective film were changedbefore and after the storage test. Therefore, from the respectiveinventive examples shown on [table 1] to [table 5], it is possible toestimate the changes of recording sensitivity in various compositions.

Although the present invention is characterized in that AgCu alloy orAgCuPd alloy contain more than one kind of any one of Al, Ti, Fe, Ni,Mo, W, it is to be expected that the above-mentioned alloy can containV, Cr, Mn, Co, Y, Zr, Nb, Ru, Ta which are transition metals havingsimilar chemical nature in addition to such added chemical elements withsimilar effects to those of the present invention being achieved.

The optical recording medium according to the present invention is notlimited to the optical recording mediums having information recordinglayers of single layer and two layers and the present invention cansimilarly be applied to optical recording mediums having multilayerstructures in which information recording layers of more than threelayers, for example, are laminated to one another.

Further, while the substrate comprising the optical recording medium isformed by injection molding in the above-mentioned examples, the presentinvention is not limited to the above-mentioned examples and can also beapplied to the case of an optical recording medium in which very smallindentations are formed on a plate having a smooth surface by 2P (Photopolimerization).

Furthermore, while the examples of the disc-like and disk-shaped opticalrecording mediums have been described so far in the above-mentionedexamples, the present invention is not limited to those examples and canbe applied to optical recording mediums of various shapes such as acard-like optical recording medium and a sheet-like optical recordingmedium as well.

DESCRIPTION OF REFERENCE NUMERALS

-   1 first substrate-   2 second substrate-   3 transparent adhesive layer-   10 optical recording medium-   11 first very small indentations-   12 second very small indentations-   13 translucent reflective film-   14 reflective film-   21 first information recording layer-   22 second information recording layer-   41 first dielectric layer-   42 recording layer-   43 heat adjustment film-   44 second dielectric layer-   45 reflective film-   100 optical recording medium-   101 substrate-   102 very small indentations-   104 magneto-optical recording layer-   105 information layer-   106 protective film-   200 optical recording medium-   201 first substrate-   202 second substrate-   203 transparent adhesive layer-   211 first very small indentations-   222 second very small indentations-   223 translucent reflective film-   224 reflective film-   231 first information recording layer-   232 second information recording layer

1. In an optical recording medium including at least an informationrecording layer and a reflective film, an optical recording mediumcharacterized in that said reflective film is made of an AgCu containingalloy containing Cu the content of which is greater than or equal to 2.0[atomic %] and less than or equal to 9.0 [atomic %] and said AgCucontaining alloy is made of an AgCu containing either of ternary alloyand quaternary alloy containing one or two chemical elements of Fe, Ni,Mo, W and whose total content of said chemical elements is greater thanor equal to 0.5 [atomic %] and less than or equal to 8.1 [atomic %]. 2.In an optical recording medium in which at least a first informationrecording layer and a second information recording layer are laminatedto each other, an optical recording medium characterized in that saidfirst information recording layer has a translucent reflective filmformed thereon, said second information recording layer has a reflectivefilm formed thereon, said translucent reflective layer is made of anAgCu containing alloy containing Cu the content of which is greater thanor equal to 2.0[atomic %] and less than or equal to 9.0[atomic %], saidAgCu containing alloy is made of an AgCu containing either of ternaryalloy and quaternary alloy containing one or two chemical elements ofFe, Ni, Mo, W and whose total content of said chemical elements isgreater than or equal to 0.5[atomic %] and less than or equal to8.1[atomic %] and information is reproduced from said second informationrecording layer with irradiation of light that has passed through saidfirst information recording layer.
 3. In an optical recording mediumincluding at least an information recording layer and a reflective film,an optical recording medium characterized in that said reflective filmis formed of an AgCuPd containing alloy thin film containing Cu thecontent of which is greater than or equal to 1.5 atomic % and less thanor equal to 9.0 atomic % and Pd the content of which is greater than orequal to 0.1 atomic % and less than or equal to 2.0 atomic % said AgCucontaining alloy is made of an AgCuPd containing either of quatemaryalloy and quinary alloy containing one or two chemical elements of Al,Ti, Fe, Ni, Mo, W and whose total content of said chemical elements isgreater than or equal to 0.5 atomic % and less than or equal to 8.1atomic %.
 4. In an optical recording medium in which at least a firstinformation recording layer and a second information recording layer arelaminated to each other, an optical recording medium characterized inthat said first information recording layer has a translucent reflectivefilm formed thereon, said second information recording layer has areflective film formed thereon, said translucent reflective film is madeof an AgCuPD containing alloy containing Cu the content of which isgreater than or equal to 1.5 atomic % and less than or equal to 9.0atomic %, and Pd the content of which is greater than or equal to 0.1atomic % and less than or equal to 2.0 atomic % said AgCuPd containingalloy is made of an AgCuPd containing either of quatemary alloy andquinary alloy containing one or two chemical elements of Al, Ti, Fe, Ni,Mo, W and whose total content of said chemical elements is greater thanor equal to 0.5 atomic % and less than or equal to 8.1 atomic % andinformation is reproduced from said second information recording layerwith irradiation of light that has passed through said first informationrecording layer.
 5. An optical recording medium according to claim 2, or3, wherein said first information recording layer is formed on a firstsubstrate molded by transparent material, said second informationrecording layer is formed on a second substrate, said first and secondsubstrates are laminated to each other through a transparent adhesiveagent layer in such a manner that information recording layers thereofare facing to each other and information is reproduced from said firstand second information recording layers with irradiation of light fromsaid first substrate side.